The present invention relates in general to improving the current load of a gas discharge lamp, and particularly to a predetermined size shield for an electrode or cathode for improving performance.
Low pressure gas discharge lamps, such as fluorescent lamps and germicidal lamps, have been known for many years. Gas discharge lamps usually have an envelope or a vessel enclosing electrodes that function as a cathode and anode. Ionized gas between the cathode and anode create an electromagnetic radiation discharge. In a fluorescent lamp, this discharge is converted to visible light. In a germicidal lamp, the ultraviolet radiation is used to disinfect materials such as wastewater.
While cathode shields of different structures have been utilized in the past to limit the loss of emission material from the cathode caused by ion bombardment and vaporization, prior cathode shields have not improved current load without changing discharge characteristics of the lamp. Prior cathode shield structures have increased the service life of a fluorescent lamp and have reduced the blacking of the inside of the lamp. However, these prior cathode shields may also increase the starting voltage of the fluorescent lamp. Therefore, there is a need for a cathode shield for use in a gas discharge lamp that can improve the current load without changing discharge characteristics.
The present invention comprises a cathode shield for use in a gas discharge lamp that has predetermined openings proportional to the size of the lamp and shield resulting in improved current load without changing discharge characteristics of the gas discharge lamp, as well as improving lamp life. A gas discharge lamp has a quartz envelope or vessel having a predetermined diameter. An electrode placed within the envelope or vessel has a cup shaped shield placed around the electrode or filament. The cup shaped shield has a large opening adjacent the end of the gas discharge lamp. A cover placed on the cup shaped shield has a hole therein. The diameter of the hole in the cover has a proportional relationship to the diameter of the envelope or vessel and the diameter of the cup shaped shield. Specifically, the ratio of the diameter of the envelope or vessel to the diameter of the hole in the cover is between 3.5 and 4.5, and the ratio of the diameter of the cup to the diameter of the hole in the cover is between 2.0 and 3.0. These proportional relationships have been found to reduce the cross sectional area of the arc at the anode or electrode, thereby increasing ion and electron current density and effectively cooling the anode. This allows for increased current load. The temperature cooling effect of the present invention also decreases the evaporation rate of cathode emission material, resulting in less consumption of emission material and longer cathode life.
Accordingly, it is an object of the present invention to improve current load without changing discharge characteristics of a gas discharge lamp.
It is a further object of the present invention to improve lamp life.
It is an advantage of the present invention that heat is dissipated.
It is another advantage of the present invention that lower temperature operation may be obtained and anode fall is reduced.
It is a feature of the present invention that a hole in a cover of a shield is sized in proportion to the lamp envelope and cup shaped shield.
It is a further feature of the present invention that a hole is placed in the cup shaped shield opposite the cover so that amalgam placed on the stem of the lamp becomes accessible.
These and other objects, advantages, and features will become more readily apparent in view of the following detailed description.